"Bent housings" or "subs" are commonly used in well drilling in order to deviate the borehole from vertical to a desired angle. "Housings" are short threaded sections of drill pipe. They are "bent" either by physical bending or machined to create an angular offset between the respective ends of the housing. When the bent housing is placed in the drill string, the bend in the housing causes the drill string to deviate from vertical as drilling progresses. One drawback in the use of bent housings is that the angle is fixed. This means that numerous bent housings must be kept at the drill site to provide a selection of a range of angles which may be required as drilling progresses. The trend in the industry has, therefore, been to develop a single bent housing on which the angle can be adjusted. The angle of the present housing is adjusted prior to insertion into the well, and remains fixed until withdrawn and readjusted. Housings of this type are therefore referred to as "surface adjustable" bent housings, to distinguish them from housings that are "downhole adjustable", that is, adjustable while in the well bore without being withdrawn to the surface.
Although the terms "subs" and "housings" are sometimes used synonymously, a "sub" is typically a bent section installed in the drill string above the downhole motor/bearing assembly/drill bit combination used in the directional drilling of well bores. A "housing" on the other hand fits between the motor and the bearing assembly and in addition to providing bend, it also accommodates a drive shaft connecting the motor to the bearing assembly/drill bit through its central bore. The present invention is intended for use primarily as an adjustable bent "housing".